Sucker feet marks on poly plates...

[Al Ferrari]

A very minor correction to your post is that in both metal and poly plates the photosensitive emulsion runs against the blanket. But the two differ in both the toughness of that emulsion and in the sensitivity of the plate surface on press.

We should be thankful to Alois for his direct personal participation in this thread as opposed to the posting of pdfs from third parties.

Al

 

[MSLDoug]

I have to disagree with that statement. Metal plates are coated with a photosensitive coating that is removed in the non image area leaving raw aluminum. The image area still has the coating on it but is covered with ink. With polyester the non image area is the photographic emulsion with the silver removed or neutralized. With polyester the plate is developed as an emulsion in photographic chemistry, metal is processed and the coating is removed in the non image area. With thermal process-less plates the coating is pulled off of the plates by the ink system which leaves the raw aluminum in the non-image area.

 

[Al Ferrari]

In my 7:45 post I say "... that in both metal and poly plates the photosensitive emulsion runs against the blanket." and i proceed to comment that " the two differ in both the toughness of that emulsion and in the sensitivity of the plate surface on press."

In your 7:30 post you say that "With polyester plates you are running the photographic emulsion directly on the blanket."

In your 8:12 post you say "With polyester the non image area is the photographic emulsion with the silver removed or neutralized."

I don't think there's any substantial disagreement. I should have been more careful, and you could be more consistent, but we are both trying to draw attention to the difference in sensitivity of the respective non image surfaces to debris on the blanket.

Al

 

[Alois Senefelder]

Fundamentals

Fundamentals

Hello MSLDoug,

The physics are of secondary importance. In Lithography we are dealing with the

chemistry of surfaces, the most important being - Inter-Facial Tensions between the

Oleophilic/Hydrophilic areas of the plate.


Polyester Plates have poor Oleophilic/Hydrophilic areas, whereas Pre-sensitised

Aluminium Plates have ideal properties.

Al Ferrari,

The PDFs I post come from authoritative sources or would you rather rely

on the Readings of Tea Leaves via Clairvoyant, supplied by a third party?


Regards, Alois

 

[Al Ferrari]

Alois,

I often find your pdfs very useful indeed. It's just that I would like the real you to take part in our discussions.

Al

 

[MSLDoug]

When did this go from trying to help someone with a problem to who knows more about things that have no relevance? Sorry I got sucked in.

 

[Alois Senefelder]

Fundamentals - again

Fundamentals - again

Hello MSLDoug,


It has a great deal of relevance - if you don't know the fundamental

cause of the problems, you are unable to be of help, I suggest you stay and learn and hopefully contribute.



Regards, Alois


" From knowledge to competence is a great step - from ignorance to competence

an even greater one"